In electrophotographic image forming apparatuses and electrostatic recording apparatuses, an electrostatic latent image or a magnetic latent image formed on an image bearing member is developed with a toner to form a visible image. Specifically, in electrophotographic image forming apparatuses, an electrostatic image (a latent image) is formed on a photoreceptor, and the electrostatic latent image is developed with a toner to form a toner image on the photoreceptor. After the toner image is transferred onto a recording medium such as paper, the toner image is fixed to the recording medium by a method such as heating and the like.
Such a toner includes a binder resin as a main component, which is made from petroleum resources. Petroleum resources have problems such that the resources will be depleted in near future; and consumption of a large amount of petroleum resources emits a large amount of carbon dioxide to the atmosphere, resulting in global warming.
By using resins derived from vegetables, which grow by absorbing carbon dioxide in the atmosphere, for the binder resin of toner, carbon dioxide only circulates in the environment, thereby making it possible to solve the above-mentioned problems at the same time.
There is a proposal for a toner for use in electrophotography, which includes polylactic acid as a binder resin. Polylactic acid can be synthesized by subjecting lactic acid to dehydration condensation or by subjecting lactide to ring-opening polymerization.
However, when polylactic acid is used as a binder resin of toner, it is difficult for the toner to have a good combination of low temperature fixability and high temperature preservability.
There is another proposal for a toner, which includes a binder resin and a colorant and which is prepared by being granulated in an aqueous medium. The binder resin is a block copolymer including a polyester skeleton A including a unit obtained by subjecting CH3—C*—H(—OH)(COOH) to dehydration condensation in the repeat unit thereof, and another polyester skeleton B not including the unit obtained by subjecting CH3—C*—H(—OH)(COOH) to dehydration condensation in the repeat unit thereof. In this regard, the optical isomer ratio (i.e., enantiomer excess) X(%), which is defined as |X(L-isomer)−|X(D-isomer)|, is not greater than 80%, wherein X(L-isomer) represents the percentage of the L-isomer lactic acid monomer and X(D-isomer) represents the percentage of the D-isomer lactic acid monomer.
It is desired for such a binder resin to have good pigment dispersing ability.
For these reasons, the inventors recognized that there is a need for a toner which can solve the above-mentioned problems and which has a good combination of low temperature fixability, high temperature preservability, and pigment dispersing property.